I recently replaced the scope on one of my rifles, but had inadvertently switched the two screws (one long, one short) that tie down the front Leupold scope mount. The longer screw was only a few thousandths of an inch longer than the short screw hole (that was supposed to hold the short screw), but just long enough to barely contact the lugs, causing a drag on the bolt that appeared about half-way on the down-stroke. I was going to take it to the gunsmith, until I did some thinking about why the problem had suddenly started, and realized it must have had something to do with the way I mounted the scope. After I switched the screws to their proper holes, the problem disappeared. I had not noticed the problem right away because I had just replaced the scope, put the rifle away, and had not worked the bolt until a couple of months later. It had not occurred to me right away that the problem might have been related to the scope base mounting screws.